Mix flour with cornflour. Add egg, sugar, vanilla sugar and 200g butter, process with the dough hook on an electric mixer. Wrap and chill for 1 hour.
Preheat oven to 200 C / Gas 6.
Roll out the dough and cut out 4cm circles.
For the marzipan topping: Knead together 250g butter, marzipan, flour, eggs, salt and lemon zest. Transfer to a piping bag and pipe circles around the edges of the biscuits. Put a blob of redcurrant jelly in the middle of each biscuit.
Place on a greased baking tray and bake for 15-20 minutes in preheated oven.